The present invention relates to postage meters (or "franking machines") having a print head that is removably mounted on a base and in which the print head has a print drum that carries printwheels. In such machines the invention relates more particularly to the device for setting the printwheels.
In conventional manner, such printwheels are mounted to rotate relative to the drum so as to enable their positions to be set, providing postage is not actually being printed. These printwheels project slightly from the periphery of the drum and they rotate together with the drum for the purpose of printing both fixed and variable postage information on each revolution of the drum. The printwheels are used for printing variable information concerning the postage amount and the date of franking. The print drum therefore carries two sets of printwheels for such variable information, which wheels project from the drum through appropriate openings in an engraved plate for printing a postage flier. The engaged plate fits around the periphery of the drum and carries fixed postage information in the form of a postage "stamp", a mention of the home post office, or another information. The same drum generally also carries an additional "advertising" engraved plate that is analogous to the first but that is generally removably mounted and that is used for printing fixed advertising information. In some machines, other print means such as one or more removable blocks are associated with the drum.
Document FR-A-2 335 002 describes a franking machine of the above-specified type having a device for setting the value printwheels with each printwheel being under manual control. That device comprises appropriate transmission means that are identical and that are disposed between each printwheel and its control means, the transmission means being constituted by driving gear wheels coupled to one another and to manual control means, and one or more driven gear wheels that are coupled to one another and to the corresponding printwheel, together with two racks that are coupled to each other and to one of the driven gear wheels and to one of the driving gear wheels.
Other postage meters no longer use manual control for setting the positions of the printwheels, but instead they use automatic control. Such automatic control is performed from a keypad of the machine and by means of logic control circuits connected to a drive motor and to one of the driving gear wheels as mentioned above.
In a postage meter having a removable head, the device for controlling the position settings of the various printwheels is mounted together with motors for performing this function and located within the print head. This makes the print head relatively bulky and heavy, thus making it more difficult to transport. In addition, a removable print head is a security module into which access by the user or by any other person not authorized by the postal authority is forbidden. Consequently, an authorized person is required whenever a maintenance problem arises relating specifically to the device for setting the printwheels, which device is complex and has a large number of parts.
In order to avoid such drawbacks, there has already been proposed, in document FR-A-2 665 782 (corresponding to U.S. Pat. No. 5,163,366, a device for setting the printwheels in the head of a postage meter, in which the head is removable relative to a base and includes a print drum fitted with said printwheels and carried on a "front" end of a sleeve whose other or "rear" end projects behind the head, and the base has a front emplacement for the head and includes a drive mechanism and control circuit referred to as a "control card" coupled to the drive mechanism and a rotary spindle coupled to the drive mechanism and projecting in part into the emplacement for the head in order to receive said sleeve thereon and to drive the drum, said device comprising:
a driving assembly having at least one control motor and at least one driving gear wheel, said assembly being coupled to said control card; PA1 a plurality of driven gear wheels, each coupled to one of the various printwheels, mounted therewith inside the head; and PA1 a plurality of sliding rods having "front" and "rear" racks, the rods being mounted in said head with the front rack of each rod engaging on one of the driven gear wheels and transmitting a command thereto as received from the driving assembly. PA1 the driving assembly is mounted in the base, in an interface housing immediately behind the front emplacement for the head, and at the periphery of the spindle and of the sleeve engaged on said spindle; and PA1 the rear racks of the sliding rods project at least in part behind the head and engage the rear end of the sleeve in the base; PA1 said driving assembly thus being suitable for engaging the rear racks of said rods and constituting a control module in said base for setting the printwheels of the head. PA1 said drive system is a rotary gear system constituting a gear train; PA1 said driving gear wheels are coaxial and parallel, together forming a block of substantially cylindrical outline, and said motors are disposed on a circular arc around said block so as to co-operate therewith to form said setting control module; PA1 said control module is mounted to pivot between a rear, retracted position in which said driving gear wheels are disengaged and remote from the respective gear trains included in the head, and a front, extended position in which the same gear wheels are in respective positions where they mesh with the same gear trains; and PA1 said control module is mounted on one or more resilient supports connecting it to its pivot axis.
According to that document FR-A-2 665 782:
That device still suffers from the drawback of being insufficiently compact and of being insufficiently convenient and flexible for positioning purposes.
The use of racks constitutes a drawback since a rack can be moved back-and-forth only, and cannot be moved continuously. Thus, as a result, if it is desired to display a "0" on a given printwheel after it has been used to print a "9", then it is necessary to cause the associated rack to run along its entire stroke. Overall, the amount of time required for setting is large.